Hi Dan,
If you have multiple clients and have to manage all these customers tenant with security as paramount task, I will suggest you to review Microsoft Lighthouse solution and this is for all the multi tenant deployments check this page - https://learn.microsoft.com/en-us/azure/lighthouse/concepts/cross-tenant-management-experience
The architecture solution is here - https://learn.microsoft.com/en-us/azure/lighthouse/concepts/architecture
Hope this helps.
JS
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